Technical Q and A for classic motorcycle maintenance and repair.
Editor’s note: If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.
Setting ignition timing
Q: I plan on installing an electronic ignition in my 1965 Triumph Bonneville this spring, although it’s been running just fine with points. My question deals with setting the timing. The primary cover on this bike does not have a plug/cover to remove so that a timing light can be used. What is the proper method used to set final timing under these conditions? — Rich Reed/Colgate, Wis.
A: Much will depend on the brand of electronic ignition you choose, but you can set static timing using piston position as a reference. Your Bonneville has a maximum advance of 39 degrees before top dead center and the auto advance unit’s range (marked on the back) should be 12 degrees. The usual formula from Triumph for timing was to double the auto advance range and subtract that from the maximum advance. In this case that would be 39-24=15. Fifteen degrees is the static advance setting. Using a table I found in the service manual for your machine, that translates to 0.068in (1.73mm). That is how far before top dead center (TDC) you want the piston when setting the timing. You can use a TDC tool if you have one or — carefully — a piece of stiff wire. Make sure the wire is long enough it won’t fall into the cylinder when the piston drops, and don’t leave it in the cylinder as you rotate the engine: you risk bending the wire or tangling with the valves. Remove the valve adjustment covers on the right cylinder so you can tell when that cylinder is coming up on compression. Rotate the engine with the kickstart, watching the intake valve. Once it opens and closes, the compression stroke is coming up. Put your finger over the spark plug hole and you’ll feel the air being compressed. Insert your measuring wire. Rotate the engine until it’s at TDC on the compression stroke. Find a reference point, insert the wire and mark it at TDC and again at 1.73mm higher than TDC. Roll the engine backward until your mark is at the reference point. Install the electronic ignition pickup. This should get you close enough to get the engine running. Once the engine is running you can use a timing light to check the position of the electronic ignition trigger as it passes the pickup at the engine speed the ignition manufacturer specifies. If you find the timing off slightly, adjust the pickup plate as you would a points plate. MC